Folliculogenesis (the growth of an ovarian follicle from the primordial stage to ovulation) is a more prolonged event than is widely appreciated, requiring more than 220 days in humans. The vast majority of this time is spent as a preantral follicle, yet very little is known about the regulation of the growth and development of these follicles. Members of the TGFbeta growth factor family induce distinct quantifiable effects in preantral follicles in culture. Deletion of the TGFbeta family signaling molecule, Smad3 results in decreased number of preantral follicles and infertility in the mouse. Follicles deficient in Smad3 do not respond normally to FSH treatment. The overall goal of this research is to determine the regulators of early follicle development. This proposal will determine the role of Smad3 in early follicle development by achieving the following aims. Specific Aim 1- Is Smad3 essential for optimal preantral follicle growth in response to FSH? This aim will determine quantitative and qualitative changes in FSH-stimulated preantral follicle growth and development in the ovary of the Smad3 deficient mouse compared to wild-type. Specific Aim 2- Does Smad3 impact FSH stimulation of granulosa cell function? This aim will use granulosa cell culture techniques to determine the integrity of the FSH signaling pathway in the absence of Smad3 and the effects of direct modulation of Smad2 and Smad3 function on FSH signaling. Specific Aim 3 - Does manipulation of Smad3 function modulate FSH-stimulated early follicle growth? In this aim we will restore Smad3 function to Smad3 deficient preantral follicles to determine if FSH responsiveness is restored. We will also directly manipulate Smad2 and Smad3 function to determine the independent and combined roles of Smad2 and Smad3 in regulating preantral follicle development. The elucidation of the mechanisms of regulation of early follicle growth, differentiation and apoptosis has profound implications for developing new non-hormonal contraceptives and treatments for ovarian causes of infertility. Additionally, the ability to manipulate the rate of loss of follicles from the finite pool of ovarian follicles could impact the timing of menopause and ovarian aging. Increased knowledge of the determinants of healthy early follicle development will also benefit the emerging field of ovarian cryopreservation and in vitro follicle development.